1. Field of the Invention
This invention relates to circuit interrupters and, more particularly, to circuit breakers including a trip mechanism, such as a ground fault and/or an arc fault trip mechanism.
2. Background Information
Circuit breakers are generally old and well known in the art. Examples of circuit breakers are disclosed in U.S. Pat. Nos. 5,260,676; and 5,293,522.
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which is heated and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. An armature, which is attracted by the sizable magnetic forces generated by a short circuit or fault, also unlatches, or trips, the operating mechanism.
In many applications, the miniature circuit breaker also provides ground fault protection. Typically, an electronic circuit detects leakage of current to ground and generates a ground fault trip signal. This trip signal energizes a shunt trip solenoid, which unlatches the operating mechanism, typically through actuation of the thermal-magnetic trip device. See, for example, U.S. Pat. Nos. 5,260,676; and 5,293,522.
Recently, there has been considerable interest in also providing protection against arc faults. Arc faults are intermittent high impedance faults which can be caused, for instance, by worn insulation between adjacent conductors, by exposed ends between broken conductors, by faulty connections, and in other situations where conducting elements are in close proximity. Because of their intermittent and high impedance nature, arc faults do not generate currents of either sufficient instantaneous magnitude or sufficient average RMS current to trip the conventional circuit interrupter. Even so, the arcs can cause damage or start a fire if they occur near combustible material. It is not practical to simply lower the pick-up currents on conventional circuit breakers, as there are many typical loads, which draw similar currents and would, therefore, cause nuisance trips. Consequently, separate electrical circuits have been developed for responding to arc faults. See, for example, U.S. Pat. Nos. 5,224,006; and 5,691,869.
Arc fault circuit interrupters (AFCIs) and ground fault circuit interrupters (GFCIs) can function as a conventional circuit interrupter (e.g., thermal-magnetic) without connecting a pigtail to the line neutral bus. Without this neutral connection, the AFCI or GFCI electrical trip circuit is not powered. As a result, this allows improper use of the circuit interrupter in which it supplies power to a load without providing arc fault or ground fault protection.
An open neutral condition, which is defined in Underwriters Laboratories (UL) Standard PAG 943A, may exist with the electrical wires supplying electrical power to GFCI devices. If an open neutral condition exists with the neutral wire on the line (versus the load) side of the GFCI device, then an instance may arise where a current path is created from the phase (or hot) wire supplying power to the GFCI device through the load side of the device and a person to ground. In the event that an open neutral condition exists, some GFCI devices which have tripped, may be reset even though the open neutral condition may remain.
U.S. Pat. No. 6,040,967 discloses a resettable GFCI receptacle that includes a reset lock-out mechanism to prevent the resetting of electrical connections between input and output conductors if the circuit interrupting mechanism used to break the connection is non-operational or if an open neutral condition exists. U.S. Pat. No. 6,040,967 states that the reset lock-out mechanism can be included in resettable circuit interrupting devices, including GFCIs, AFCIs, immersion detection circuit interrupters and appliance leakage circuit interrupters. A test button is used to activate a test cycle, which tests the operation of the circuit interrupting mechanism. A reset button is used to activate a reset cycle, which reestablishes electrical continuity between the input and output conductive paths or conductors. While the reset button is being depressed, reset contacts are closed to complete a test circuit so that the test cycle is activated. During the test cycle, a plunger moves a banger upwardly so that the banger strikes a latch member pivoting a latch finger while the latch member continues to move. As a result, the latch finger is lifted over one side of the remote end of a movable contact arm onto the other side thereof. After tripping, a coil assembly is de-energized so that the plunger returns to its original extended position, and the banger releases the latch member so that the latch finger is in a reset position. Release of the reset button causes the latching member and movable contact arm to move until the contacts are closed.
There is room for improvement in circuit breakers. There is also room for improvement in circuit breakers employing a line neutral connection to power a trip circuit.